1. Field of the Invention
The present invention relates to a dual time/frequency generation apparatus for generating normal time and frequency signals even if trouble occurs in a main time/frequency generator by substituting the main time/frequency generator having the trouble with a sub time/frequency generator in a code division multiple access (CDMA) system.
2. Discussion of Related Art
A time/frequency generation apparatus in a CDMA system usually Internally includes a rubidium oscillator as an independent time generator and keeps a standard time by continuously comparing an its internal time with came information received from satellites in a global positioning system (GPS) and correcting an internal time and time length. Each satellite in the GPS has extremely accurate cesium and rubidium atomic clocks and provides an extremely accurate measurement of time. The time/frequency generation apparatus generates Lime data, Time of Day (TOD), according to the time information received from the GPS satellite via a GPS receiver, 10 MHz frequency (synchronizing reference frequency in the CDMA system), and a time clock (1 pulse per second: 1 PPS). The TOD, as time data which is generated every even seconds by the time/frequency generation apparatus, is a signal Including information or time such as second, minute, hour, day, and year, and information about normal or abnormal operation status of the time/frequency generation apparatus. 10 MHz frequency is a generation signal of the rubidium which is adjusted based upon the time information received from the GPS satellite. A 1 PPS time clock is a signal produced by dividing 10 MHz by 10 million.
Such time/frequency generation apparatus in the CDMA system is implemented in a dual system to promote accuracy and reliability of the system. FIG. 1 is a block diagram of a conventional dual time/frequency generation apparatus in the CDMA system. As shown in the drawing, the dual time/frequency generation apparatus includes: a first time/frequency generator 1 for generating time/frequency signals such as TOD, 10 MHz frequency, and 1 PPS signal; a second time/frequency generator 2 for generating the same time/frequency signals as the output signals of the first time/frequency generator 1 in order to continuously provide the time/frequency signals to the CDMA system even when trouble occurs in the first time/frequency generator 1; and a time/frequency output unit 5 for selectively outputting the signals from the first and second time/frequency generators 1 and 2 through manual operation.
The time/frequency output unit 5 includes: a first switch 6 for selecting one of the first TOD and second TOD respectively outputted by the first and second rime/frequency generators 1 and 2 through external operation; a second switch 7 for selecting one of the first and second time clocks IC respectively outputted by the first and second time/frequency generators 1 and 2 through external operation; and a third switch 8 for selecting one of the first and second 10 MHz frequencies respectively outputted by the first and second time/frequency generators 1 and 2 through external operation.
Operation of such conventional dual time/frequency generation apparatus in the CDMA system is as follows. The first time/frequency generator 1 which is selected as a main generator generates the time/frequency signals and the second time/frequency generator 2 which is selected as a spare generates the same time/frequency signals through the same operation as that of the first time/frequency generator 1, the time/frequency signals cannot be provided to the CDMA system, which makes the whole system stop. A system operator then selects the second time/frequency generator 2 as the main one and makes the second time/frequency generator 2 provide the time/frequency signals to the CDMA system by manually operating the first to third switches 6 to 8 in the time/frequency output unit 5.
By employing a spare time/frequency generator in addition to a main one, even when one time/frequency generator has trouble, the other normal time/frequency generator performs the same function, thereby minimizing impact of abnormal time/frequency signals to the CDMA system.
However, in the conventional dual time/frequency generation apparatus of the CDMA system, since the system operator manually switches from the main time/frequency generator to the sub one after sensing the malfunction of the main time/frequency generator, the abnormal time/frequency signals, such as time jump and frequency jump, can be outputted.
Moreover, even if errors occur in just ore signal of the TOD, 10 MHz frequency, and 1 PPS time clock, the whole time/frequency generator is switched, thereby reducing an average life of the system.